Rechargeable battery

ABSTRACT

In a rechargeable battery in which an electrode plate group ( 10 ) obtained by superimposing a positive electrode plate ( 1 ), in which positive electrode material ( 1   a ) is attached to a positive electrode current collector ( 1   b ), and a negative electrode plate ( 2 ), in which negative electrode material ( 2   a ) is attached to a negative electrode current collector ( 2   b ), with a separator ( 3 ) therebetween is accommodated in a battery container ( 4 ) together with electrolyte, the current collectors ( 1   b   , 2   b ) of the electrode plates ( 1, 2 ) are respectively projected at opposite ends of the electrode plate group ( 10 ), forming by themselves flat planes ( 11, 12 ) by being pressed, and current collecting plates ( 8, 9 ) are joined to these flat planes ( 11, 12 ).

REFERENCE TO RELATED APPLICATION

This is a divisional application of application Ser. No. 09/719,323,filed Jan. 4, 2001, and now issued as U.S. Pat. No. 6,818,025 B1.

TECHNICAL FIELD

The present invention relates to rechargeable batteries, and inparticular to rechargeable batteries wherein an electrode plate groupobtained by superimposing a positive electrode plate, in which positiveelectrode material is attached to a current collector, onto a negativeelectrode plate, in which negative electrode material is attached to acurrent collector, with a separator therebetween, is accommodated in abattery container together with electrolyte.

BACKGROUND ART

In recent years, there has been rapid progress in reducing the size andweight of electronic equipment, which has increased demands to reducethe size and weight and increase the capacity of the batteries used astheir power sources.

To meet these demands, lithium ion rechargeable batteries employing acarbon-based material as the negative electrode active material and atransition metal oxide containing lithium, such as LiCoO₂, as thepositive electrode active material have been put into practice byvarious companies. Lithium rechargeable batteries in which metalliclithium or lithium alloy is employed as the negative electrode activematerial had the problem that the lithium precipitated on the negativeelectrode as charging proceeded. On the other hand, lithium ionrechargeable batteries are free of such problem and so have excellentcycle characteristics. As a result, there has been vigorous developmentof lithium ion rechargeable batteries and their use in electronicequipment has become more common.

Lithium rechargeable batteries are studied also as a means for solvingglobal environmental problems or energy problems. As a way ofguaranteeing power stability while maintaining a good globalenvironment, implementation of technology for load equalization isdesired; considerable benefits in terms of load equalization could beexpected if use of small-scale battery power storage devices capable ofstoring power during the night could be made common in ordinaryhouseholds etc. In order to prevent atmospheric pollution by car exhaustgases and global warming due to CO₂, it would also be desirable toextend the use of electric vehicles in which some or all of the motivepower is obtained by rechargeable batteries. Large lithium ionrechargeable batteries with a cell capacity of about 100 Ah aretherefore being developed for use as battery power storage devices fordomestic use and as power sources for electric vehicles.

The construction of such a lithium ion rechargeable battery is shown inFIG. 5. An electrode plate group 30 constituted by superimposing apositive electrode plate 21, in which positive electrode material 21 ais attached to a positive electrode current collector 21 b, and anegative electrode plate 22, in which negative electrode material 22 ais attached to a negative electrode current collector 22 b, wound inspiral fashion with a separator 23 therebetween are accommodated in abattery container 24 comprising a battery case 25 and a battery closure26 together with electrolyte. A positive electrode current collector tab28 with one end joined to a suitable location of the positive electrodecurrent collector 21 b has its other end connected to the inner surfaceof the battery closure 26 constituting the positive electrode terminal,while a negative electrode current collector tab 29 with one end joinedto a suitable location of the negative electrode current collector 22 bhas its other end connected to the inside bottom surface of the batterycase 25 constituting the negative electrode terminal. An insulatingpacking 27 is interposed between the inner circumference of the top endaperture of the battery case 25 and the outer circumference of thebattery closure 26 so as to mutually insulate the battery case 25 andthe battery closure 26 and to seal the battery container 24.

However, since current was extracted from a single location of apositive electrode plate 21 and a negative electrode plate 22 throughcurrent collecting tabs 28 and 29 in this structure, the averagedistance from the positive electrode plate 21 and negative electrodeplate 22 to the current collecting tabs 28 and 29 was long. Moreover,the area of current collecting tabs 28 and 29 was small, so theirelectrical resistance was large and the current collecting efficiencywas poor. Furthermore, since the current collecting efficiency was poor,there was the problem that charging and discharging with large currentsresulted in increased battery temperatures, which shortens the life ofthe rechargeable battery.

Laid-open Japanese Patent Application No. 8-115744, for example,discloses an electrode plate group which is directed to solve theseproblems. In this electrode plate group, current collectors arerespectively projected at one side of the electrode plates, withrespective leads being attached to the leading ends of these projectedportions of the current collectors. Therefore when the electrode platesare wound in spiral fashion, the leads and the end edges of the currentcollectors respectively form a positive electrode end face and anegative electrode end face at opposite ends of the electrode plategroup. Both terminals are connected to the positive electrode end faceand the negative electrode end face respectively. However, suchstructure is subject to the problem of high cost, since leads arerequired and the manufacturing steps are complicated.

Laid-open Japanese Patent Application No. 10-21953 discloses anarrangement in which current collectors of both electrode plates projectrespectively on opposite sides and their tips make resilient pressurecontact with the positive electrode terminal and negative electrodeterminal. However, the connection between the current collectors and theterminals is only effected by the elastic restoring force of the tips ofthe current collectors, which are bent at an acute angle within acertain range of elasticity. Therefore, the electrical connection isunstable, and the output of the battery also lacks stability underconditions of use in which it is subjected to vibration.

In view of the above problems of the prior art, an object of the presentinvention is to provide a rechargeable battery wherein the efficiency ofcurrent collection is high, the rise in temperature duringcharging/discharging can be reduced, and in which charging/dischargingcan be achieved in a stable fashion with an inexpensive construction.

DISCLOSURE OF THE INVENTION

A rechargeable battery according to the present invention comprises: anelectrode plate group including a positive electrode plate, in which apositive electrode material is attached to a current collector, anegative electrode plate, in which a negative electrode material isattached to a current collector, the positive and negative electrodeplates being superimposed with an intervening separator therebetween,wherein the current collector of one or other of the positive electrodeplate and the negative electrode plate is projected on at least one sideof the electrode plate group for forming by itself a flat plane on oneside of the electrode plate group; an electrolyte; a battery containerin which the electrode plate group and the electrolyte are accommodated;and a current collecting plate joined to the flat plane formed at oneside of the electrode plate group. Since the current collecting plate isjoined to the flat plane formed by a side portion of the currentcollectors, the current collection efficiency is high and the rise intemperature during charging/discharging can be kept small. Furthermore,since the flat plane is formed by the current collector itself, theconstruction can be made inexpensive. Moreover, the construction isstable with respect to vibration etc since the current collecting plateis welded to the flat plane of the current collector, so charging anddischarging can be effected in a stable fashion.

If the positive electrode plate and the negative electrode plate arewound in spiral fashion with the separator interposed therebetween, withtheir current collectors being respectively projected at opposite endsof the electrode plate group thereby forming respective projectedportions, flat planes can be formed at opposite ends of the electrodeplate group efficiently by pressing the projected portions of thecurrent correctors at opposite ends of the electrode plate group indirections along the winding axis of the electrode plate group.

The current collecting plate may be arranged in contact with each of theflat planes and laser-welded in the radial direction at a plurality oflocations in the circumferential direction, so that a large number oflocations of the side edges of the current collectors can be integrallywelded in a simple fashion to the current collecting plates, making itpossible to achieve high current collection efficiency with an easyoperation.

Alternatively, a plurality of ribs may be formed on the currentcollecting plate such as to protrude towards the projected portions ofthe current collectors, the flat planes being formed by pressing theribs against the projected portions of the current collectors, and thecurrent collecting plate being welded to each of the current collectorsat these ribs, so that the current collector plates make reliablecontact with the current collectors at these ribs and they can be weldedtogether even more reliably.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an axial cross-sectional view of a rechargeable batteryaccording to one embodiment of the present invention;

FIG. 2 is an axial cross-sectional view of an electrode plate group inthis embodiment in a step wherein a flat plane is formed by theprojected portion of a current collector;

FIG. 3 is a perspective view of the electrode plate group in thisembodiment in a step in which the current collecting plate is joined tothe flat plane of the current collector;

FIG. 4 is a perspective view of a modified example of current collectingplate in a state welded to the electrode plate group in the rechargeablebattery according to the present invention; and

FIG. 5 is an axial cross-sectional view of a rechargeable batteryaccording to an example of the prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

A lithium ion rechargeable battery according to an embodiment of therechargeable battery of the present invention is described below withreference to FIG. 1 to FIG. 3.

In FIG. 1, reference numeral 1 represents a positive electrode plate andreference numeral 2 represents a negative electrode plate. An electrodeplate group 10 is constituted by winding in spiral fashion the positiveelectrode plate 1 and the negative electrode plate 2 in a mutuallyopposed condition with a separator 3 made of microporous polyethylenefilm therebetween. This electrode plate group 10 is accommodated withina battery container 4 together with electrolyte. The battery container 4comprises a battery case 5 which is of cylindrical enclosure shape andconstitutes an negative electrode terminal, and a battery closure 6constituting a positive electrode terminal. An insulating packing 7 isinterposed between the inner circumference of the top aperture of thebattery case 5 and the outer circumference of the battery closure 6,whereby mutual insulation is effected therebetween and the batterycontainer 4 is sealed. The separator 3 is interposed also between theelectrode plate group 10 and the inner circumference of the battery case5.

The positive electrode plate 1 is constituted by coating both surfacesof a positive electrode current collector 1 b with a positive electrodematerial 1 a; a side part (in the example illustrated, the top part) ofthis positive electrode current collector 1 b projects from the portionthat is coated with the positive electrode material 1 a. The negativelectrode plate 2 is constituted by coating both surfaces of negativeelectrode current collector 2 b with a negative electrode material 2 a;a side part opposite from the projected portion of the positiveelectrode current collector 1 b (in the example illustrated, the bottompart) of this negative electrode current collector 2 b projects from theportion that is coated with the negative electrode material 2 a. Theseparator 3 projects to the outside beyond both side edges of the coatedportions of the positive electrode plate 1 and the negative electrodeplate 2.

The side edge of the positive electrode current collector 1 b thatprojects further than the separator 3 is elastically deformed byapplying pressure thereto, whereby a flat plane 11 is formed. A positiveelectrode current collecting plate 8 is joined to this flat plane 11.Likewise, the side edge of the negative electrode current collector 2 bthat projects further than the separator 3 is elastically deformed byapplying pressure thereto, whereby a flat plane 12 is formed, and anegative electrode current collecting plate 9 is joined to this flatplane 12. The positive electrode current collecting plate 8 and thenegative electrode current collecting plate 9 are respectively connectedto the battery closure 6 and the battery case 5. Reference numerals 8 aand 9 a respectively denote connecting strips extending from the outercircumference of the current collecting plates 8 and 9 for connectingthem to the inside surface of the battery closure 6 and the insidebottom surface of the battery case 5, respectively.

A detailed description of the positive electrode plate 1, the negativeelectrode plate 2, and the electrolyte will now be given. The positiveelectrode current collector 1 b is made of aluminum foil or the like.The positive electrode plate 1 is constituted by coating both surfacesof the positive electrode current collector 1 b with a positiveelectrode material 1 a containing a positive electrode active materialand a binder. For the positive electrode active material, LiCoO₂,LiMn₂O₄, LiNiO₂, any other lithium oxide in which one of Co, Mn or Ni issubstituted with another transition metal, or a lithium-containingtransition metal oxide other than these may be used. In particular,Mn-based lithium-containing transition metal oxides such as the globallyabundant low-cost LiMn₂O₄ are suitable.

The negative electrode current collector 2 b is made of copper foil orthe like, and the negative electrode plate 2 is constituted by coatingboth surfaces of the negative electrode current collector 2 b with anegative electrode material 2 a containing a negative electrode activematerial and a binder. For the negative electrode active material,carbon-based materials such as graphite, petroleum coke, carbon fiber,or organic polymer sintered products, or metals or oxides, or compositematerials of these capable of occluding and releasing lithium, may beused.

The electrolyte may be obtained by dissolving a lithium salt such aslithium hexafluorophosphate (LiPF₆), lithium perchlorate (LiClO₄), orlithium fluoroborate (LiBF₄) into a non-aqueous solvent such as ethylenecarbonate (EC), propylene carbonate (PC), diethylene carbonate (DEC) orethylene methyl carbonate (EMC), either alone or in combination, at aconcentration of 0.5 mol/dm³ to 2 mol/dm³.

To give a specific example, electrolyzed manganese dioxide (EMD:MnO₂)and lithium carbonate (Li₂CO₃) were mixed at a ratio Li/Mn=1/2 andsintered in the atmosphere of 800° C. for 20 hours, whereby LiMn₂O₄ wasproduced as the positive electrode active material. The positiveelectrode material 1 a was then obtained by mixing, by weight, 92%LiMn₂O₄, 3% acetylene black serving as conducting agent, and 5%polyfluorovinylidene as binder. In order to knead the positive electrodematerial 1 a into the form of a paste, the polyfluorovinylidene servingas the binder was employed in the form of N-methylpyrrolidonedispersion. The mixing ratios given above are ratios in terms of thesolid fractions. Both faces of the positive electrode current collector1 b made of 20 μm thick aluminum foil were coated with this positiveelectrode material paste such that positive electrode material layerswere formed except a region of width 10 mm on one side edge, which wasleft uncoated. The film thickness of both positive electrode materiallayers was the same and the sum of the two film thicknesses aftercoating and drying was 280 μm, giving a positive electrode platethickness of 300 μm. After this, the positive electrode plate 1 wascompressed using a press roll of diameter 300 mm, to reduce thethickness of the positive electrode plate 1 to 200 μm. The density ofthe positive electrode material was then 3.0 g/cm³.

For the negative electrode material 2 a, a mixture of artificialgraphite and styrene butadiene rubber (SBR) as a binder in a weightratio of 97:3 was employed. In order to knead the negative electrodematerial 2 a into the form of a paste, the styrene butadiene rubberbinder was employed in the form of an aqueous dispersion. The abovemixing ratios are expressed as solid fractions. Both faces of thenegative electrode current collector 2 b made of 14 μm thick copper foilwere coated with this negative electrode material paste such thatnegative electrode material layers were formed except a region of width10 mm on one side edge, which was left uncoated. After this, thenegative electrode plate 2 was compressed using a press roll of diameter300 mm, to reduce the thickness of the negative electrode plate 2 to 170μm. The density of the negative electrode material was then 1.4 g/cm³.

The electrolyte was obtained by dissolving lithium hexafluorophosphate(LiPF₆) as solute in a concentration of 1 mol/dm³ in a solvent obtainedby mixing ethylene carbonate (EC) and diethylene carbonate (DEC) in avolume blending ratio of 1:1.

These positive electrode plate 1 and negative electrode plate 2 thusproduced are opposed to each other with an intervening separator 3therebetween and wound around in spiral fashion to form an electrodeplate group 10, in such a manner that the portions of the currentcollectors 1 b, 2 b which were left uncoated project at opposite ends ofthe electrode plate group 10. This electrode plate group 10 is insertedand arranged in position in a molding jig 13 of cylindrical enclosureshape as shown in FIG. 2, and is subjected to pressure by a pressingmember 14 from one end aperture of the molding jig 13. Thereby, theprojected portions of the current collectors 1 b, 2 b are elasticallydeformed to be bent radially inwards substantially at 90° as shown bythe phantom lines, whereby flat planes 11, 12 are formed at oppositeends of the electrode plate group. Since the positive electrode plate 1and the negative electrode plate 2 are wound in spiral fashion, theprojected portions of the current collectors 1 b, 2 b are not bentradially outwards. Rather, all of the projected portions of the currentcollectors are uniformly and progressively bent radially inwards. As aresult, although folding may occur to some extent, they are as a wholedeformed together into flat planes 11, 12.

Next, the electrode plate group 10 formed with flat planes 11, 12 isremoved from the molding jig 13 and, as shown in FIG. 3, the currentcollecting plates 8, 9 are pressed into contact with the flat planes 11,12, and these are laser welded together by irradiating a plurality oflocations in the circumferential direction of the surfaces of thecurrent collecting plates 8, 9 with a laser beam 15 in radial fashionfrom the middle towards the outer periphery. After this, the electrodeplate group 10 with these current collecting plates 8, 9 joined theretois accommodated within the battery case 5 and vacuum-impregnated withthe electrolyte. The current collecting plates 8, 9 are connected bylaser welding etc to the battery closure 6 and the battery case 5,respectively, and the battery case 5 is sealed with the battery closure6.

As described above, the electrode plate group 10 in this lithium ionrechargeable battery is constituted by winding in spiral fashion apositive electrode plate 1 and a negative electrode plate 2 with aseparator 3 therebetween, such that the current collectors 1 b, 2 b ofthe two electrode plates respectively project at opposite ends thereofand the current collecting plates 8, 9 are joined to the flat planes 11,12 formed by the projected portions of the current collectors 1 b, 2 b.Accordingly, the efficiency of current collection is high and the risein temperature during charging/discharging can be kept small.Furthermore, since the flat planes 11, 12 are formed by the currentcollectors 1 b, 2 b themselves, the construction can be made of lowcost. Furthermore, the construction is stable with respect to vibrationetc, because these flat planes 11, 12 are welded to the currentcollecting plates 8, 9, so charging and discharging can be effected in astable fashion.

Since the flat planes 11, 12 for joining the current collecting plates8, 9 are formed by applying pressure to both ends of the electrode plategroup 10 in the direction along the core of the winding axis, they canbe formed efficiently.

The current collecting plates 8, 9 are pressed towards the flat planes11, 12 and subjected to laser welding in the radial direction at aplurality of locations in the circumferential direction in this tightlypressed condition. Therefore, integral welding of a large number oflocations of the side edges of the current collectors 1 b, 2 b to thecurrent collecting plates 8, 9 can be achieved in a straightforwardfashion, enabling high current collection efficiency to be achieved withease of operation.

In the description of the above embodiment, an example was given inwhich the entire surface of the current collecting plates 8, 9 was offlat plate shape. FIG. 4 illustrates a modified example of a currentcollecting plate 8 or 9, in which a plurality of ribs 16 are formedprojecting towards the projected portions of the current collectors 1 b,2 b of the electrode plate group 10 in radial fashion. Laser welding iseffected along these ribs 16 under a condition in which the currentcollecting plates 8, 9 are pressed toward the electrode plate group 10such that these ribs 16 bite into the projected portions of the currentcollectors 1 b, 2 b so as to form the flat planes 11, 12.

If such ribs 16 are provided on the current collecting plates 8, 9 andlaser welding is conducted with these being pressed against theprojected portions of the current collectors 1 b, 2 b, the flat planes11, 12 formed by the projected portions make reliable contact with thecurrent collecting plates 8, 9 through the ribs 16, whereby the currentcollecting plates 8, 9 and the current collectors 1 b, 2 b can be weldedtogether even more reliably.

INDUSTRIAL APPLICABILITY

As will be clear from the above description, with the rechargeablebattery of the present invention, the current collector of one or otherof the electrodes projects on at least one side of the electrode plategroup, a flat plane being formed at the tip of this projected portion byitself, and a current collector plate is welded to this projectedportion of the current collector. Accordingly, the current collectionefficiency is high and the rise in temperature duringcharging/discharging can be made small. Since the flat plane is formedby the current collector itself, an inexpensive construction can beachieved, and since the current collecting plate is joined to the flatplane, the construction is stable with regard to vibration etc. Thepresent invention thereby realizes an inexpensive structure forelectrode plate group with which the battery exhibits excellent currentcollection efficiency and stable charging/discharging characteristics.

1. A method of manufacturing a rechargeable battery, comprising thesteps of: interposing a separator between a positive electrode plate anda negative electrode plate to form a multilayer electrode structure,said positive electrode plate and said negative electrode plateincluding uncoated end portions; winding said multilayer electrodestructure in spiral fashion to form an electrode plate group having aspiral configuration, said positive electrode plate, said negativeelectrode plate and said separator being positioned relative one anotherprior to the winding of said multilayer structure such that after beingwound the uncoated end portions of said positive electrode plate andsaid negative electrode plate extend respectively from opposite ends ofthe electrode plate group thereby defining uncoated projected portions:providing a current collecting plate having a circular shape and aplurality of ribs extending radially with respect to a center of thecircular shape, the ribs projecting from a base plane surface of thecollecting plate, the ribs having opposing side regions extending fromthe base plane surface at an inclination with respect to the base plane,the ribs having flat regions interconnecting the opposing side regionsand displaced apart from the base plane surface of the currentcollecting plate by the opposing side regions; contacting at least oneof the opposite ends of the electrode plate group with the currentcollecting plate such that the circular shape covers an overall area ofthe spiral configuration of the one of the opposite ends of theelectrode plate group; pressing the current collecting plate onto theelectrode plate group such that the uncoated projection portions aredeformed into flattened areas in contact area portions whereat thecurrent collecting plate contacts the uncoated projection portions, theribs are pressed into the uncoated projected portions in the contactarea portions, the uncoated projected portions are deformed intoflattened areas by the flat regions of the ribs, and the flattened areasextend generally orthogonal to the winding axis.
 2. The method ofmanufacturing a rechargeable battery according to claim 1, furthercomprising the step of welding the current collecting plate to theelectrode plate group at a plurality of locations within the flattenedareas deformed by the ribs to form an electrode plate group assembly. 3.The method of manufacturing a rechargeable battery according to claim 2,wherein the current collecting plate includes a positive currentcollecting plate and a negative current collecting plate, said step ofwelding includes welding the positive and negative current collectingplates on respective ones of the opposite ends of the electrode plategroup corresponding to the positions of the uncoated projected portionsof the positive electrode plate and the negative electrode plate to formthe electrode plate group assembly.
 4. The method of manufacturing arechargeable battery according to claim 3, further comprising the stepsof: accommodating said electrode plate group assembly in a battery case;and vacuum-impregnating the electrode plate group assembly within thebattery case with an electrolyte.
 5. The method of manufacturing arechargeable battery according to claim 4, further comprising the stepsof: connecting the current collecting plates each to a respective one ofa battery closure and the battery case; and sealing the battery casewith the battery closure.